That’s a good point.

I re-ran numbers using:

— PPG for Team A above average in other 14 games as my 1st input
— PPG allowed for Team A_opp below average in other 14 games as my 2nd input
— Points above average scored by Team A against Team A_opp as my output

I forced the constant to be zero; the best-fit formula was 0.622*Team A + 0.469*Team A_Opp

Based on your very rough estimate, you would expect the coefficients to equal close to 2 (i.e., we just say the Patriots are 12.6 PPG above average, the Titans are 7.0 points below average, therefore NE should score 19.6 points more than average when playing TEN.) As it turns out, the coefficients only add up to 1.1. Interesting.

The more on-point issue for this post would be that the ratio of Team A to Team A_Opp is 57%, in line with our other numbers. You should also check out Neil’s post today: http://www.footballperspective.com/another-note-on-the-relative-impact-of-offense-vs-defense-on-scoring/